The invention is directed to a process to prepare metal nanoparticles or metal oxide nanoparticles.
US-A-2010/0072434 describes a process to prepare gold nanoparticles by first preparing a polymer surfactant in an alcohol solvent and heated to its boiling point. To the boiling mixture a metal seed, i.e. chloroplatanic acid is added and subsequently HAuCl4 salt is added after which gold nano particles form around the seed.
WO-A-2007/055663 describes a process to prepare a metal nano particle wherein a metal precursor compound is contacted with a reducing agent and a capping agent to generate a reaction mixture. Exemplified metal precursor is HAuCl4, exemplified reducing agent is NaBH4 and the exemplified capping agent is amino acid. To this mixture sonication is applied to generate a plurality of metal colloidal particles and depositing the metal particles on a support, i.e. TiO2, to prepare a catalyst.
US-A-2009/0325795 describes a process to prepare platinum nanoparticles wherein first a chemical compound like potassium tetrachloroplatinate is prepared. To this compound potassium iodide (KI) is added and subsequently the mixture is reduced to form the platinum nanoparticles.
At the heart of all known methods developed to make nanoparticles lies the reduction reaction of metal cations. The art is to limit the number of reduced cations per nanoparticle and keep its size as constant as possible, and that is invariably achieved by adding extra chemical stabilizers—most methods of nanoparticles synthesis involve micelles or colloids. These contaminate the final product and adversely affect its performance, e.g. in catalysis or biological applications. In addition, the prior art processes have the problem that they involve multiple chemical synthesis steps. Furthermore these processes require additional chemicals to act as for example reducing agent, capping agent, polymer and/or a surfactant.
In a paper titled ‘The Phenomenon of the Formation of Metallic Dust from Cathodes’ as read by Prof. Dr. Fritz Haber at the Second Meeting of the American Electrochemical Society on Sep. 17, 1902 an experiment was described wherein black clouds form around a lead cathode when the direct current density is increased. The same is observed for tin, bismuth, thallium, arsenic, antimony and mercury. The same paper mentions that in an acid solution a platinum wire cathode becomes black and spongy. Starting with the same platinum cathode in an alkaline solution only a slightly roughened surface was observed.
US-A-2009/0218234 describes a process to prepare titania nanowires by applying an electrical potential between an anode and a cathode as part of an electrolytic cell. The surfaces of both anode and cathode comprise a titanium surface.